Pressure switch



Feb. 12, 1963 c. M. BLACKBURN PRESSURE SWITCH F iled Aug. 10. 1960INVENTOR.

N R w K C A L B M w M H C ATTORNEYS 3,077,524 PRESSURE SWITCH Charles M.Blackburn, Silver Spring, Md., assignor to the United States of Americaas represented by the Secretary of the Navy Filed Aug. 10, 1960, Ser.No. 48,790 2 Claims. (Cl. 200-82) The present invention relates topressure swiches and more particularly to such a switch that is operablein conjunction with a unique hydraulic actuator arrangement.

Well known in the art are pressure switches which will actuate when apredetermined fluid pressure is attained. Such switches may also beprovided with a mechanical latch or detent to hold the switch open orclosed after actuation, although oftentime the latch or detent isomitted whereby subsidence of the prmsure will allow the switch toreturn by the force of a spring to its original condition.

These prior art devices are directly responsive to the rate of change ofthe fluid pressure, and because of this, are not satisfactory for use inan environment where the fluid pressure is likely to fluctuate,particularly if it is desired that the switch remain open or closedduring the period of pressure fluctuation, and yet be able to return tothe original condition upon subsidence of the pressure below a certainvalue.

It is therefore the object of the present invention to provide a fluidpressure actuated switch which will actuate at a predetermined value ofpressure, remain in the actuated position even after subsidence of thepressure below the predetermined value, and be able to return to theoriginal position after the pressure has subsided to a secondpredetermined value. Other objects and many of the attendant advantagesof this invention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing.

Briefly the present invention contemplates a stepped piston including apair of unequal area piston faces and enclosed within a cylinder havinga pair of corresponding bores. The piston faces are disposed such thatthe one of smaller area is subjected to the fluid pressure before theother. As the pressure increases to a predetermined amount the piston isurged against the force of a spring into an actuating position wherein arod attached to the piston engages a pair of electrical contacts inswitch closing fashion. While the piston is in this position, a bypassport is opened to allow access of the fluid pressure to the second andlarger piston face thus allowing a lesser value of pressure to maintainthe piston in the actuating position. The rod then is held in a switchclosing position even though the fluid pressure fluctuates considerably.As the pressure decreases to a second predetermined value where itbecomes insufficient by acting on the larger piston area to counteractthe force of the spring, the piston is returned to its originalposition.

The single drawing is a simplified schematic diagram of an applicationof the present invention, the switch being shown in enlarged crosssection.

The particular application depicted relates to missiles and specificallyto the arming of a warhead of such a missile, although it will becomeobvious that the present invention may be employed in other ways.

Referring to the drawing in detail, a switch 2 is shown included in anarming circuit 4 and a self-datruct circuit 6 of a missile 8. The switchcomprises a cylinder '10 and a contact housing 12, the former beingadapted to receive fluid pressure from a pump 14 that is coupled to ahydraulic system 16 of the missile and driven by a ram air turbine 17.Threadably secured to the housing 12 and closing the end thereof is acap 18. The cylinder in- 3,077,524 Patented Feb. 12, 1963 ice eludescylinder elements 19 and 20 which are coupled in threaded engagement, aseal being provided therebetween.

Fluid pressure developed by the pump 14 is delivered through a line 26to a first chamber 28 of relatively small bore within the cylinder 10.At the opposite end of the chamber 28 is formed a concentric secondchamber 29 of larger bore which communicates with the first chamber. Abypass port 30 is provided in the cylinder 10 and serves to permit fluidto be delivered to the second chamber 29 from the first chamber 28.

A stepped piston 31 is disposed within the cylinder 10 and is formedwith a piston face 32 that coacts with the chamber 28, and a second face34 which coacts with the second chamber 29. Projecting concentricallyfrom the piston 31 is a rod 36 which extends through an apertured wall38 of the cylinder 10 into the contact housing 12. A spring 40 ispositioned on the rod 36 and is interposed between the wall 38 and thepiston 31, the action of the spring tending to maintain the piston tothe right in a non-depressed position. While the piston 31 is in thisnon-depressed position, the bypass port 30 is blocked thereby, the portbeing unblocked when the piston moves to the left under influence offluid pressure into a depressed position.

Provided on the piston 31 to minimize fluid leakage are seals 42 and 44,another seal 46 being recessed in the wall 38 for contact with the rod36.

The contact housing 12 is threadably secured to the wall 38 of thecylinder 10 and encloses the projecting end of the rod 36. Supportedwithin the housing 12 are pairs of contacts 50 and 52 that areengageable with the rod 36. As can be seen from the drawing, when thepiston 31 is in the non-depressed position, the rod 36 engages thecontacts 52 to close a portion of the self-destruct circuit 6, it beingrecognized that actual self-destruction of the missile will not occuruntil certain other conditions have been met. In the depressed position,the piston 31 urges the rod 36 into engagement with the contacts 50 toclose the arming circuit 4. Positioned on the rod 36 is an insulatingsleeve 54 which is located in such manner that when the rod is inengagement with the contacts 50, the connection across the contacts 52is disrupted by the interposition of the insulating sleeve.

In operation when the fluid pressure being delivered to the line 26 iszero or very nearly so, the force of the spring 40 is of sufficientmagnitude to constrain the piston 31 in the non-depressed position sothat only the selfdestruct contacts 52 are in engagement with the rod36. This condition corresponds to a pre-boost or pre-launch condition ofthe missile where the arming circuit 4 should be kept open. While inthis non-depressed position, the piston 31 blocks the bypass port 30 sothat the fluid pressure is exerted only on the piston face 32.

After the missile is launched, the ram air driven turbine 17 causes thepump 14 to build up hydraulic pressure in the line 26 and on the pistonface 32. As the speed of the missile is increased, the hydraulicpressure increases until a value thereof is attained which issufficient, while acting on the small area of the piston face 32, tomove the piston 31 against the force of the spring 40 until thedepressed position is attained where the seal 44 is seated against thewall 38. In this position, the rod 36 engages the contacts 50 tocomplete the arming circuit 4, the contacts 52, however, beinginterrupted by the insulating sleeve so that the self-destruct circuitis kept open. Also, when the piston 31 is in this depressed position,the bypass port is unblocked so that the fluid pressure now exerts forceadditionally on the piston face 34. This then permits a much lower valueof the fluid pressure to maintain the piston 31 in the depressedposition, since a considerably greater piston area is acted on thereby.

3 Thus, if for any reason, as for example in high altitude maneuvering,the hydraulic pressure from the pump 14 should fluctuate, the armingcircuit 4 will remain a closed, insofar as the switch 2 is concerned.

If the hydraulic system should fail completely, then the lack of fluidpressure in the chambers 28 and 29 will allow the spring 40 to returnthe piston 31 to the non-depressed position where the contacts 52 areagain closed to permit self-destruction of the missile.

It will be noted from the drawing that a definable gap is providedbetween the peripheral wall of the piston face 34 and the inner wall ofthe chamber 29. It is also to be noted that the seal 44 is not aperipheral seal but a face seal positioned for seating against the endWall 38. The purpose of this arrangement is to allow any fluid which mayleak by the seal 42, when the switch 2 is in the pre-boost ornon-depressed position, to find a path around the piston face 34 andeventually flow out of the chamber 29 through a drain 60 in the end wall38. Otherwise, such fluid leaking by the seal 28 might tend toaccumulate in the chamber 29 ahead of the piston face 34 and causepremature actuation of the switch.

Similarly, in order to accommodate any fluid which might leak by theseal 46 and to otherwise vent the contact housing 12, an aperture 62 isformed in the wall thereof.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A pressure switch, comprising, a cylinder having a pair of adjacent,aligned chambers therein, one of said chamber-s being substantiallysmaller in bore than the other, means for supplying fluid pressure tothe smaller of said chambers, a differential piston disposed within saidchambers and responsive to said fluid pressure to be moved thereby fromthe smaller chamber toward the larger chamber to a depressed position,said piston including a relatively large portion disposed within thelarger of said chambers and having a relatively large piston facethereon, and a relatively small portion disposed within the smaller ofsaid chambers and having a relatively small piston face thereon exposedto said fluid pressure, each of said piston portions having a diameterslightly less than the diameter of the chamber in which it is disposed,and both of said piston faces being directed away from said depressedposition, resilient means in said cylinder for producing a force on saidpiston counter to that produced by said fluid pressure and formaintaining said piston in a non-depressed position in the absence ofsaid fluid-pressure, two spaced pairs of contacts mounted on saidcylinder, a movable switch element on said piston and successivelyengageable with said pairs of contacts in a switch closing position whensaid piston is moved toward a depressed position, and an insulatingmeans on said movable element and engageable with one pair of saidcontacts for preventing concurrent closure of both pair of said contactswhen said piston is in said depressed position, said cylinder having abypass .port extending from the smaller chamber to the larger chamberfor supplying fluid pressure to said latter chamber for acting on saidrelatively large piston face, the inlet end of said bypass port beingpositioned so that it is closed by the smaller portion of said pistonwhen the piston is in said non-depressed position but is automaticallyopened when said piston moves to said depressed position.

2. A pressure switch as recited in claim 1, wherein a slight, unsealedclearance exists between said larger piston portion and the wall of saidlarger chamber, and including seal means between the smaller pistonportion and the wall of the smaller bore and positioned to seal saidbypass port from said'fluid pressure until said piston moves toward saiddepressed position.

References Cited in the file of this patent UNITED STATES PATENTS747,772 Rick-man Dec. 22, 1903 1,952,667 Geraghty Mar. 27, 19342,596,171 Rabinow May.13, 1952 2,764,645 Smith Sept. 25, 1956 2,813,177Eberhard et al Nov. 12, 1957 2,827,850 Muzzey Mar. 25, 1958 2,891,120S'aholt June 16, 1959 2,982,093 Belcher et al. May 2,1961

1. A PRESSURE SWITCH, COMPRISING, A CYLINDER HAVING A PAIR OF ADJACENT,ALIGNED CHAMBERS THEREIN, ONE OF SAID CHAMBERS BEING SUBSTANTIALLYSMALLER IN BORE THAN THE OTHER, MEANS FOR SUPPLYING FLUID PRESSURE TOTHE SMALLER OF SAID CHAMBERS, A DIFFERENTIAL PISTON DISPOSED WITHIN SAIDCHAMBERS AND RESPONSIVE TO SAID FLUID PRESSURE TO BE MOVED THEREBY FROMTHE SMALLER CHAMBER TOWARD THE LARGER CHAMBER TO A DEPRESSED POSITION,SAID PISTON INCLUDING A RELATIVELY LARGE PORTION DISPOSED WITHIN THELARGER OF SAID CHAMBERS AND HAVING A RELATIVELY LARGE PISTON FACETHEREON, AND A RELATIVELY SMALL PORTION DISPOSED WITHIN THE SMALLER OFSAID CHAMBERS AND HAVING A RELATIVELY SMALL PISTON FACE THEREON EXPOSEDTO SAID FLUID PRESSURE, EACH OF SAID PISTON PORTIONS HAVING A DIAMETERSLIGHTLY LESS THAN THE DIAMETER OF THE CHAMBER IN WHICH IT IS DISPOSED,AND BOTH OF SAID PISTON FACES BEING DIRECTED AWAY FROM SAID DEPRESSEDPOSITION, RESILIENT MEANS IN SAID CYLINDER FOR PRODUCING A FORCE ON SAIDPISTON COUNTER TO THAT PRODUCED BY SAID FLUID PRESSURE AND FORMAINTAINING SAID PISTON IN A NON-DEPRESSED POSITION IN THE ABSENCE OFSAID FLUID PRESSURE, TWO SPACED PAIRS OF CONTACTS MOUNTED ON SAIDCYLINDER, A MOVABLE SWITCH ELEMENT ON SAID PISTON AND SUCCESSIVELYENGAGEABLE WITH SAID PAIRS OF CONTACTS IN A SWITCH CLOSING POSITION WHENSAID PISTON IS MOVED TOWARD A DEPRESSED POSITION, AND AN INSULATINGMEANS ON SAID MOVABLE ELEMENT AND ENGAGEABLE WITH ONE PAIR OF SAIDCONTACTS FOR PREVENTING CONCURRENT CLOSURE OF BOTH PAIR OF SAID CONTACTSWHEN SAID PISTON IS IN SAID DEPRESSED POSITION, SAID CYLINDER HAVING ABYPASS PORT EXTENDING FROM THE SMALLER CHAMBER TO THE LARGER CHAMBER FORSUPPLYING FLUID PRESSURE TO SAID LATTER CHAMBER FOR ACTING ON SAIDRELATIVELY LARGE PISTON FACE, THE INLET END OF SAID BYPASS PORT BEINGPOSITIONED SO THAT IT IS CLOSED BY THE SMALLER PORTION OF SAID PISTONWHEN THE PISTON IS IN SAID NON-DEPRESSED POSITION BUT IS AUTOMATICALLYOPENED WHEN SAID PISTON MOVES TO SAID DEPRESSED POSITION.